As a conventional electric-power conversion system, a technology disclosed in Patent Document 1 is known. As illustrated in FIG. 17, the conventional electric-power conversion system includes a diode bridge 12 connected with an AC power source 1 by way of a main relay 10; an inverter circuit 14 connected with the rear stage of the diode bridge 12 by way of an inrush current prevention resistor 4 and a reactor 13 and formed of a single-phase inverter configured with a DC voltage source 19, diodes 15 and 16, and semiconductor switching devices 17 and 18; and a smoothing capacitor 22 connected with the rear stage of the inverter circuit 14 by way of a rectifier diode 20 and a short-circuiting switch 21.
A charging relay 2a is connected in parallel with the inrush current prevention resistor 4. The positive electrode of the smoothing capacitor 22 is provided between the inrush current prevention resistor 4 and the reactor 13, by way of a discharging resistor 11 and a discharging relay 5a. In addition, reference numerals 31, 32, and 33 denote a rectified voltage detection circuit, a DC voltage detection circuit, and a smoothing capacitor voltage detection circuit, respectively.
In the conventional electric-power conversion circuit configured in such a manner, full wave rectification is applied to an AC input from the AC power source 1 and then is inputted to the inverter circuit 14 by way of the reactor 13. The inverter circuit 14 PWM-controls an input current from the diode bridge 12 in such a way that the power factor of the input from the AC power source 1 becomes approximately “1” and accumulates energy in the DC voltage source 19; concurrently, the inverter circuit 14 makes the DC voltage across the smoothing capacitor 22 keep track of a predetermined target voltage. Such a conventional electric-power conversion system can improve the input power factor and reduce the power loss and noise.